The present invention relates to a safety arrangement and in particular to a piece of equipment provided with a safety arrangement.
In industry, for example, a wide range of equipment is used. The equipment often requires some form of power to operate. The equipment may be electrically powered, pneumatically powered or hydraulically powered, for example. The equipment may be moveable, or be a machine with moving parts. A typical example of electrically powered equipment used in both light and heavy industry is the conveyor. A conveyor is a mechanical device for conveying articles or materials during manufacture, processing or packaging. A specific example of a conveyor is a conveyor belt, which is an endless moving belt made of rubber, canvas, etc., and which is used to convey articles or materials from one place to another.
Conveyor belts are widely used and have a wide variety of applications. A conveyor belt may be used in a small-scale commercial environment, for example in a self-service restaurant. A conveyor belt may also be used in a large-scale heavy industrial environment, such as in the quarrying and mining industries. A conveyor belt utilizes a continuously moving belt of material to convey material from one location to another. The belt is moved by rotating rollers or the like. It is quite possible that a user of the conveyor belt, or somebody working in the environment in which the conveyor belt is used, could get caught in the conveyor belt. If the user is caught in the conveyor belt, they can cause the conveyor belt to become jammed, or, in some situations, be injured by the conveyor belt. While this problem may not be so prevalent in applications where the conveyor belt is relatively small and low powered, this problem can be particularly relevant to industrial applications where the conveyor belts used are generally larger and more powerful.
In the quarrying and mining industries, for example, the conveyor belts used need to be both large (to be able to convey large volumes of material), and powerful (to be able to convey large weights of material). Accordingly, it is an important consideration in the control and configuration of such systems to prevent unintended operator interference with the conveyor. It is for these and other reasons that safety arrangements have been designed and incorporated into equipment requiring power to operate, such as the conveyor belt. The general principal behind such safety arrangements is that when the safety control system is activated, power is prevented from being supplied to the equipment. Therefore, even if a user unintentionally interferes with operation in a conveyor belt, operation of the conveyor is interrupted.
FIG. 1 illustrates a conveyor belt provided with a prior art safety arrangement. The conveyor belt comprises a belt 1 which surrounds a plurality of rollers 2. In an elevated configuration, the belt 1 and rollers 2 are supported by supports 3. The belt 1 is made from any suitable material, such as rubber, canvas, etc.
Attached to one of the supports 3 is a safety switch 4. A rope 5 (or other elongate flexible elements, such as a cable or the like) is attached to the safety switch 4. An end of the rope 5 opposite safety switch 4 is attached to another of the supports 3 that is located remote from the support 3 to which the safety switch 4 is attached. The rope 5 extends through eyelets 6 which serve to support the rope 5 and enhance the operation of the safety arrangement, as described in more detail below. In one example of the operation of the safety arrangement, the rope 5 is arranged to be under tension, and this may be achieved via the use of a tensioning device 7 mounted on the rope 5. When the rope 5 has been put under sufficient tension, an actuator 8 provided on the safety switch 4 is moved to put the safety switch 4 in a conducting state. That is, the safety switch allows electricity to be supplied to the rollers 2 of the conveyor belt.
During operation, if a user desired to quickly suspend operation of belt 1 or rollers 2 of the conveyor belt, the user can pull on the rope 5. When the rope 5 is pulled, the tension 5 on the rope increases, and this effect is enhanced by the fact that the rope 5 passes through the eyelets 6. As a consequence of the tension on the rope 5 increasing, a mechanism within the safety switch 4 is moved to put the safety switch 4 into a non-conducting state. That is, when the rope 5 is pulled, the safety switch 4 prevents electricity being supplied to the rollers 2 of the conveyor belt. When no electricity is applied to the rollers 2 of the conveyor belt, the belt 1 stops moving. In the event a user has become undesirably entangled with the conveyor belt, pulling rope 5 terminates operation of the conveyor thereby reducing the detrimental affects of the user's interference with the conveyor. The safety of the conveyor belt has therefore been improved by the incorporation of the safety arrangement.
Although the safety arrangement illustrated in FIG. 1 does improve the safety of the conveyor belt (or other powered equipment), it does have its disadvantages. In known safety arrangements similar to that illustrated in FIG. 1, the tolerances required to keep the safety arrangement in a useful operating condition are high. For example, safety standards are often imposed on the use of such safety arrangements. A safety standard may require that the safety switch 4 moves from a conducting to a non-conducting state when the rope 5 has moved only 3 mm. Whether or not standards are imposed on the safety arrangement, it is often difficult to set up and maintain a reliable operating condition. The rope 5 needs to be accurately tensioned in order for the safety switch 4 to remain in a conducting state when the rope 5 has not been pulled, so that the conveyor belt is not stopped unless it is desired to do so.
When the conveyor belt and the safety arrangement are used outdoors, it is even more difficult to stay within the tolerances required to maintain a reliable operation condition. Thermal expansion or contraction due to variations in temperature in which the conveyor belt is used can make it difficult or impossible to set up the safety arrangement reliable operation. Furthermore, if the conveyor belt is long, the longer the rope 5 that is required. As the length of rope 5 is increased, it becomes even more difficult to accurately tension the rope 5 and ensure that it does not expand or contract to such a degree as to prevent the safety arrangement from working reliably.
Depending upon the conditions in which the safety arrangement is used, it has been found that the rope 5 can only be a maximum length of around 50 m to 150 m before it becomes too difficult to accurately and reliably set up the safety arrangement and ensure that it continues to operate reliably. The restriction on the length of the rope 5 necessarily limits the length of the conveyor belt to which a safety arrangement can be applied. If the conveyor belt is longer than 150 m in length, it becomes impractical to use a single safety arrangement as shown in FIG. 1. Although this may not be a problem in small commercial or industrial applications, where conveyor belts commonly only run for a few tens of meters, it can be a persistent and costly problem to overcome in heavy industry, where conveyor belts may extend for many kilometres. When conveyor belts extend for many kilometres a plurality of the safety arrangements of FIG. 1 must be used, as illustrated in FIG. 2. The use of a plurality of safety arrangements has a number of drawbacks. For example, the greater number of safety arrangements increases the cost associated with equipping the conveyor with a safety arrangement that runs the length of the conveyor. Also, if the conveyor belt is high above the ground, or extends across dangerous or difficult terrain, it can be difficult to determine which of the safety switches 4 has been moved to a non-conducting state to stop the conveyor belt from working. Although it may be relatively straight forward to determine which safety arrangement has been activated if an operator manually activated one of the multiple safety systems, it can be more difficult if, for example, the safety arrangement has been moved into a non-conducting state due to changes in environmental conditions, or due to rocks or trees (etc) hitting or pulling on the rope.
It is therefore an object of the present invention to obviate or mitigate at least one disadvantage of the prior art, whether mentioned above or elsewhere.